This invention relates generally to a novel low temperature steel alloy and more particularly to a steel alloy capable of affording a hardness of about HB 450-500 and a V-notch Charpy impact value at -40.degree. C. of at least about 15 ft-lbs.
When construction machines such as power shovels, wheel excavators and the like are used in extremely cold regions such as Alaska and polar regions, it is essential that parts thereof subjected to wearing and impact conditions be made of a material having improved low temperature mechanical properties.
Wear-resistant cast steels have been generally employed for such parts, which steels are obtained by the heat treatment, including hardening and tempering, of low alloy cast steels so as to impart a hardness (Brinell) of HB 400-500. Low temperature mechanical properties of the conventional cast steels, however, are not satisfactory. FIG. 1 shows the relationship between tensile strength and hardness, and Charpy impact value at -40.degree. C. in conventional heat treated low alloy cast steels, from which it will be seen that their low temperature impact value decreases with increase in their hardness. Thus, the conventional cast steels having a sufficient hardness fail to show desirable toughness, involving a danger of brittle fracture, whereas those having a sufficient low temperature impact value fail to exhibit a satisfactory hardness, and are poor in wearing resistance.